Typically, internal combustion engines utilize filters having a filter media which removes harmful particles from lubricating oil. When the filter media becomes clogged, it is desirable to change the filter, but, for one reason or another, many filters are not changed upon becoming clogged. The engine will still need to be lubricated so filters are typically provided with bypass valves. When the engine is not running, the oil is not under pressure and will therefore tend to drain back into the engine so that when the engine is again started, oil is not initially pulled from the filter element because the filter element is empty. During the time it takes to circulate oil through the filter element, there is a risk of the engine not being lubricated for a very short interval. During that short interval, the engine may suffer slight wear. A minimal number of short intervals is not significant, but as the engine is started repeatedly, the amount of time that sufficient lubricating oil is unavailable because the filter has been drained, can become rather lengthy and thus result in engine damage. In order to prevent this, dirty side anti-drainback valves are employed.
However, even when dirty side anti-drainback valves are employed, there is an opportunity for wear because clean side oil in the hollow core of the filter element has been allowed to drain away and thus there is an interval when insufficient lubricating oil is available during engine starts. Consequently, it is advisable with some engines to provide a clean side anti-drainback valve, as well as a dirty side anti-drainback valve, so that the oil filter does not contribute to engine wear due to voids in oil circulation because clean side oil has drained from the hollow core of the filter element, even though dirty side oil has been retained.
In the manufacture and supply of oil filters, most situations require only oil filters which have a dirty side anti-drainback feature and a bypass feature. Typically, this requires a filter cartridge of a first configuration. There is, however, a demand for filter elements which have both clean side and dirty side anti-drainback capabilities, and thus the manufacturer must stock a separate line of lubricating filters for this purpose. Usually, it is more inconvenient and therefore more expensive to provide two different products, if the parts for those products are not readily interchangeable, because work in process inventory is increased.